1. Field of the Invention
This invention relates to polymer bodies and, in particular, polymer bodies that include additives.
2. Art Background
Poly(vinyl chloride) (PVC) is used in an extremely large variety of applications. However, PVC itself is unstable to heat and light. To mitigate this problem, PVC is mixed with a carefully formulated stabilizer system. Unless this system is very carefully formulated, PVC exhibits processing and stability difficulties. The heat utilized to mold the polymer into a desired shape is sometimes sufficient to cause its decomposition. Additionally, stabilized PVC still has a tendency to undergo decomposition. The stability of PVC has been significantly improved by adding a variety of stabilizers. For example, it is common to utilize epoxy resins together with a barium-cadmium (Ba/Cd) phosphite or barium-cadmium-zinc (Ba/Cd/Zn) phosphite mixture to control both processing and long-term stability. Stabilizers have proven to be quite effective and are used in essentially all PVC products. Recently, however, there has been some desire to replace the epoxy resin and also cadmium-containing stabilizer system with another system.
Long-term and processing stability, however, are not the only properties which must be controlled for effective use of PVC compound. Typically, it is desirable that additives be introduced into the PVC to modify other characteristics. For example, it is desirable that the PVC compound be flame retardant, be amenable to expeditious processing, be stable in humid conditions, have heat and color stability over time, and have desirable mechanical and electrical properties. Thus, polymers such as PVC must be blended with not only stabilizers but with many additives to produce all of the desired properties. Generally, each additional additive substantially augments the price of the blended polymer. One additive often enhances one property but either degrades a second property or degrades the efficacy of other additives. For example, attempts to replace epoxy resin and cadmium systems have not been successful. Substitutes for epoxy resins yield significantly degraded stability, and substitutes for cadmium such as lead and tin stabilizers often have toxicity, color, and cost disadvantages. The predisposition of additives to separate from the polymer and coat the processing equipment is also increased as the number and amount of additives are increased. It is, therefore, extremely difficult to formulate a suitable additive system or to modify an existing additive system.
As discussed, it is quite difficult to remove and replace epoxy stabilizers. Additionally, replacement additives, even if they could be formulated, are quite likely to affect adversely other properties and to interact undesirably with other additives. As a result, an effective substitute for epoxy stabilizing systems that produce adequate stability without adversely affecting other desirable properties has not been reported.